Certain types of microemulsions are known in the art. For example, oil-in-water microemulsions or water-in-oil microemulsions are employed in the hydraulic fluid field. By way of illustration, U.S. Pat. No. 4,337,161 discloses oil-in-water microemulsions, whereas U.S. Pat. No. 4,371,447 discloses water-in-oil microemulsions for use in hydraulic fluids, and the like. T. P. Hoar and J. H. Schulman (see Nature 152 102, 1943) reported the formation of transparent water-in-oil dispersions containing oil, water, alkali-metal soap and an amphipathic substance such as amyl alcohol. Mutual solubilization of benzene and ethylene glycol by means of amphiphiles (e.g., n-dodecanol and "Aerosol OT") was disclosed by P. A. Winsor (See Transactions of the Faraday Soc., 44 376, 380 1948). It has also been proposed that the depression of interfacial tension between the oil and water phases necessary for formation of microemulsion is brought about by the spontaneous distribution of the alcohol amphiphile between the oil phase and the oil/water interfaces. (See L. Prince, J. of Colloid and Interface Sci. 23, 165 1967).
Microemulsions, sometimes referred to as micellar solutions, soluble oils or swollen micelles, have been discussed in the literature. See, for example, Microemulsions, I. D. Robb, Editor, Plenum Press (1981); Technology of Micellar Solutions by W. C. Tosch, Paper No. SPE 1847-b, Society of Petroleum Engineers of AIME (American Insitute of Mining, Metallurgical and Petroleum Engineers, Inc., 1967); and, Emulsions and Emulsion Technology by Prince, pp 125-179 (Marcell Dekker, Inc., 1974). Microemulsions are typically characterized by the prior art as clear, bright and transparent, and these characteristics are desirable for purposes of the present invention. These microemulsion characteristics are due to the fact that the particle (i.e. micro-droplet) is typically smaller than the wave-length of visible light. Although clear to the eye, the presence of the microemulsion particles can be detected by instrumental light-scattering techniques. In contrast, macroemulsions are visibly opaque.
The small size of the particles imparts properties to microemulsions that are not found in other fluid systems, particularly macroemulsions which have larger size particles. For example, water-in-oil microemulsions are typically less viscous than water-in-oil macroemulsions formed from the same base oil. This is important in a number of different applications, one of which is lubricating fluids.
The advantages of microemulsions in terms of their improved storage stability, clarity, homogeneity, ease of preparation, and lower viscosity, all as compared to conventional macroemulsions, makes the search for new types of microemulsions particularly attractive.